Brown trout Salmo trutta - Department of Agriculture, Forestry and ...

zone demarcation, while those in Mpumalanga were concerned that some of their existing farmswould be excluded.10.4 Risk summaryThere is reasonable likelihood that:There will be escapees from any established culture facility unless best managementpractises are followed;Unless barriers are provided and the environment is unsuitable, S. trutta could potentiallycolonise and establish in previously un-invaded river catchments where it is introduced andconditions are suitable;Introduced trout will compete with and/or predate on indigenous species in the area andwill pose a risk to the continued survival of native fish species especially those that arealready range rare or range restricted;No hybridisation will occur with indigenous species; andNo diseases or parasites will be introduced, if appropriate best management practises areadopted, and all individuals are certified disease free by suitably qualified veterinarians priorto introduction.11 Control and prevention optionsThere are a number of control options for limiting the introduction and spread of alien freshwaterfish species in South Africa. Brown trout have already been introduced to river systems in SouthAfrica. The focus thus needs to be on preventing their spread or deliberate introduction to newareas or river systems, as well as seeking to eradicate these fish from systems where their impactson biodiversity is considered to be unacceptably high.Controlling the spread of invasive species through prevention is thought to be the most costeffectivemeans (Leung et al. 2002). The Department of Environmental Affairs & DevelopmentPlanning Generic Environmental Best Management Practice Guideline for Aquaculture Developmentand Operation in the Western Cape (Hinrichsen 2007) should be used as a guide for construction offacilities and management thereof. These measures can serve to reduce biosecurity risks for morerisky culture techniques such as pond or cage culture from moderate to high or from moderate tolow. Key points from these guidelines are summarised below.It is recommended that all new land-based aquaculture facilities should be built above the 1 in 50year flood line and the intertidal zone, with infrastructure built to resist the impacts of floods or tidalcurrents (Hinrichsen 2007). The creation of physical barriers around the facility can also be effectivein preventing spread of invasive species (Novinger & Rahel 2003). For example, weirs can help toprevent upstream invasions (although the impacts of this construction to the ecosystem must alsobe considered prior to permit authorisation) (Driver et al. 2011). Secure fencing around theaquaculture facility in combination with restricted access will prevent any person intentionallyremoving live individuals (Hinrichsen 2007).Page | 11